Research On The Adsorption Behaviour Of Natural Zeolite To Ammonia Wastewater And Regeneration Process

The problem of ammonia nitrogen pollution is becoming more and more serious,ammonia nitrogen has became a leading indicator affecting the quality of surface water environment.Zeolite hasgoodapplication prospect in the treatement of ammonia wastewater because of its extensive sources,low-cost and high adsorption ability.This study of treating ammonia wastewater with medium-low concentration by the adsorption of natural zeolite was conducted to make this treatment process can be an effective pretreatment method before biochemical treatment system.This study was based on the absorption and desorption behaviors of natural zeolite to ammonia nitrogen and the chemical regeneration method was optimized by steam heating.In addition,the operating parameters and stability of absorption process were investigated by a pilot experiment.Specific conclusions are as follows:The adsorption process of nuatual zeolite to ammonia was endothermic and spontaneous.The pseudo second-order rate equation and langmuir isotherm model could fit the adsorption process.Ion exchange process played a main role in adsorption process and physical absorption also existed.In the ion exchange process the main exchanged cations were Na+ and Ca2+.At lower ammonia nitrogen concentration Na+ was first to be exchanged and with the increasing of ammonia nitrogen concentration the exchange capacityof Ca2+would be larger than Na+.Fe2+ had a strong inhibitory effect on the adsorption process of zeolite to ammonia nitrogen and the effect of Ni2+,Zn2+,Pb2+ was related to their concentrations.At concentration below 40mg/L,the sequence of inhibition effect was Pb2+,Zn2+,Ni2+;While,the sequence was Ni2+,Zn2+,Pb2+ over 50mg/L.The desorption experiment under static and dynamic condition indicted the optimal composition of regeneration solution was sodium hydroxide concentration 0.10mol/L and sodium chlorideconcentration 5.0%.The influence sequence of various factors on the desorption reaction was: pH,liquid-solid ratio,sodium chloride concentration,reaction time and reaction temperature,among which pH,liquid-solid ratio,sodium chloride concentration had remarkable effects on reaction.The regeneration method of combining regeneration liquid and steam heating could obtained a good result and had obviousadvantages than regenerated by using regeneration liquid alone.Regenerated the saturated zeolite by regeneration liquid alone the consumed volume of regeneration liquid wold be 16 bed volume.The consumption of combined method to obtain a complete regeneration was 2 bed volume,which was just 12.5% of 16 bed volume.During the regeneration process the weight proportion of Na could increased from 0.34% to 1.53% and the adsorptioncapacity of zeolite would not decline and still stay at a high level.Also,the regeneration process had a slight destruction to the structure of zeolite.Using natural zeolite to treat the effluent of air stripping process in an iron oxide red factory at pilot scale,the result showed it could achieved a good regeneration of zeolite at the running condition: added 0.75 bed volume regeneration liquid in three divided times,desorbed zeolite by regeneration liquid for 1h every time and heated the zeolite by steam for 2h.Under the experimental operating condition one ton natural zeolite could adsorb 4kg ammonia nitrogen and 16 ton wastewater could be treated per time,the concentration of ammonia nitrogen in wastewater could be reduced from around 300mg/L to less than 100mg/L.After 17 times regeneration,the zeolite couldmaintain stable adsorption capacity.The pilot experiment demonstrated the feasibility of treating ammonia wastewater with medium-low concentration by the adsorption of zeolite and the regeneration method of combining regeneration liquid and steam heating was fit for saturated zeolite.